The storing of a perishable commodity, such as food, for a, relatively, long period of time is a difficult problem. It is necessary to provide a storage atmosphere and which atmosphere must be, carefully, maintained. For example, the storage atmosphere must be maintained within a, relatively, narrow temperature range and also must be maintained within a, relatively, narrow relative humidity range. In certain instances, extraneous gases may be introduced into the atmosphere to slow the physiological change of the food. For example, there may be introduced into the atmosphere carbon dioxide, ethyleneoxide, or other gases to slow the maturing or ripening of the food in storage.
For example, it is desirable to store potatoes for approximately twelve months. This makes it possible to process the potatoes the entire year. The investment for the processing equipment is less than if potatoes can be stored only four months and must be processed within this four-month period. If potatoes can be stored for twelve months, it makes it possible for the processor of the potatoes to have more full utilization of the processing equipment and therefore have a lower unit cost for processing equipment for unit of processed potato.
Potatoes are a staple food and have been stored in many ways. One way potatoes have been stored and are stored is in barrels. The barrels are small units. The barrels can be stored in warehouses or in ground cellars or other appropriate housings. By storing the potatoes in barrels, the spoilage and the rotting of the potatoes is localized. If rot occurs, the rot may be limited to one barrel or only a few barrels of potatoes.
Another way of storing potatoes is in burlap bags. Again, the burlap bags are small storage units. The burlap bags may be stored in a warehouse, in a ground cellar or in other suitable housings. Again, if spoilage of potatoes occurs, the spoilage may be limited to one bag of potatoes or a few bags of potatoes.
Still another way of storage of potatoes is in bins or piles. There may be a large warehouse and the potatoes may be stored in bins 6 feet, 8 feet, 10 feet, or 17 feet in height. Or, the potatoes may be stored in piles 6 feet, 8 feet, 10 feet, or 17 feet in height, for example.
Usually, for the above-described ways of storing potatoes, the potatoes in storage are subject to the outside atmosphere. The warehouse is not heated. The ground cellar or root cellar is not heated. If the outside temperature varies, the temperature in the warehouse or root cellar will vary. Generally, speaking, the potatoes are harvested in the fall at the time of harvest when the temperature may vary from approximately 50.degree. F. to 70.degree. F. The relative humidity may vary from approximately 20 percent relative humidity to about 90 percent relative humidity, depending upon the area of the world in which the potatoes are being harvested. In winter, the potatoes are stored in the warehouse or in the ground cellar and are subject to the outside temperatures. The outside temperatures may be relatively warm such as 30.degree. or 40.degree. F. Or, the outside temperatures may be relatively cold such as minus 20.degree. F. or minus 30.degree. F. The temperature in the warehouse or in the ground cellar will correspond closely to the outside temperature. Also, the relative humidity in the warehouse and in the ground cellar will correspond closely to the relative humidity of the outside atmosphere. Further, the relative humidity of the outside atmosphere may vary considerably. At certain times, the relative humidity may be close to 100 percent and, the relative humidity in the warehouse or the ground cellar will be similar to that. If the outside temperature suddenly falls from approximately 50.degree. to approximately 10.degree. F., the relative humidity at about 10.degree. F. will be close to 100 percent but, after a few days of about 10.degree. F., the relative humidity has decreased. Further, during the winter, when the potatoes are stored, and also into the spring, the ambient temperature of the atmosphere varies over a relatively wide temperature range, alternately heating and cooling, many times during the fall, winter and spring. Likewise, the relative humidity of the ambient atmosphere varies considerably during the fall, winter and spring. The varying temperature and the varying relative humidity of the ambient atmosphere, and also of the atmosphere in the warehouse and ground cellar, has an effect on the food in storage and on potatoes in storage.
As is well known, potato is essentially a starch with a tough skin. A critical temperature for the potato is about 45.degree. F. If the temperature of the potato is reduced to a temperature less than approximately 45.degree. F., possibly, less than about 43.5.degree. F., the starch in the potato converts into a sugar. However, above about 43.5.degree. F. or, approximately, 45.degree. F., the starch in the potato remains a starch. If the potato is to be used to make fried potatoes, such as shoestring potatoes and potato chips, it is desirable to store the potato above about 45.degree. F. If the potato contains sugar, the sugar in the deep far frier burns and turns brown and the potato, shoestring potato or potato chips, all have a streaked brown color which quite often is a dark brown. Therefore, it is desirable from a commercial utilization standpoint to store the potato at a temperature of about 45.degree. F. A desirable temperature for the storing of potatoes which will be fried is a temperature in the range of about 45.degree. to approximately 50.degree. F. If the potatoes in storage are to be used for seed potatoes, it is desirable to have the potatoes at a temperature in the range of about 38.degree. to about 40.degree. F. Further, it is desirable to have the temperature of the potatoes in storage at a constant temperature and not a fluctuating temperature. If the potatoes in storage are stored at approximately 38.degree. F., and then, suddenly, placed in an atmosphere where the temperature is much above 38.degree. F., there is a physiological change in the potatoes and the potatoes begin to sprout.
In regard to relative humidity if the relative humidity of the atmosphere in which the potato is stored is a high humidity, there is less shrink of the potato. For example, if the atmosphere has a low relative humidity, there may be a 17 percent shrink of the potato. This means a 17 percent less potato for commercial utilization. As previously stated, the potato has a tough skin. If the relative humidity of the atmosphere in which the potato is stored is a low relative humidity, there is a quite large driving force for the transfer of moisture from inside the potato, through the tough skin and to the atmosphere. Therefore, it is desirable to have a high relative humitity for the atmosphere in which the potato is stored so as to lessen the transfer of the moisture from inside the potato and through the tough skin and into said atmosphere. In this regard, it is desirable to have the relative humidity of the atmosphere in the range of approximately 96 to 98 percent relative humidity. If the potato is bruised, there is the possibility of the potato rotting. If the relative humidity of the atmosphere in which the potato is stored is a low relative humidity, there is a greater possibility of rotting of the potato in the bruised area. Therefore, it is desirable, to lessen the possibility of rot, to have a relatively high relative humidity for the atmosphere. Further, rot in the potato spreads in storage by physical contact with water. If the potatoes are in contact with a pool of water, there is a greater possibility of the spread of rot than if the potatoes are not in contact with the pool of water. This leads to a critical situation whereby it is desirable to have a high relative humidity in the atmosphere in which the potatoes are stored but to have no pools of water in contact with the potatoes. This is possible by the careful introduction of moisture into said atmosphere. The moisture must be introduced as very fine droplets and not as large droplets. Upon being introduced as very fine droplets, the atmosphere readily absorbs the moisture.
One of the factors of assistance in controlling the temperature and the relative humidity in the storage facility is the building. There have been used many buildings and which buildings consist of a frame with an outside skin. The frame may be wood or steel and the skin may be wood or steel or aluminum. The roof of the building may be sloping or flat metal and may be of wood or sheet metal. Many times, in the past, the buildings have not had insulation and not had a moisture barrier. Another type of building can be a frame and block building wherein the frame is of steel and the block may brick, concrete block, cinder block, concrete tilt wall and the like. The roof may be flat or may be sloping and may have a protective composition cover. Again, there is, probably, no insulation and moisture barrier. In the storage facility or storage building, the humidity is above 90 percent and, preferably about 98 percent to 99 percent relative humidity. If there be no insulation and moisture barrier in the building, there is a possibility of the formation of liquid water on the floor. Assume that the temperature outside the storage building is 45.degree. F. and the temperature inside the storage building is 45.degree. F., the relative humidity is 98 percent. In the winter, the temperature outside the building decreases in the space of one day to 0.degree. F. Then, with no insulation, the moisture in the atmosphere inside the building, upon contacting the roof and the walls of the building, condenses and forms into drops of water which fall onto the floor of the building. The potatoes in the building in contact with the liquid water for a period of time will spoil and rot. For example, I know of such a situation wherein the potatoes are, initially, piled in piles of about 20 feet in depth inside the building. With the sudden lowering of the outside temperature, the moisture in the building condensed and ran onto the floor of the building. The potatoes in the building started to rot and the pile of potatoes settled 4 feet so that instead of the pile being 20 feet in depth, the pile was 16 feet in depth. Naturally, the result of this type of rot is a waste of the potatoes in the storage facility.
The value of this storage facility can be readily seen when it is considered that in storage, by methods and apparatus used prior to this invention, that the rotting and the spoiling of potatoes amounted to approximately 15 percent of potatoes in storage; coupled with this spoiling of the potatoes was the shrink factor of about 17 percent. Under these conditions, there could be a loss of about 30-32 percent. And, under exceptional adverse conditions, I have seen a 100 percent loss of potatoes in storage. Prior to this invention, many farmers storing potatoes could expect a loss of about 17-20 percent of the potatoes each year. If the rotting and spoiling of potatoes can be decreased by a considerable percentage due to the teachings of this invention, it is seen that considerable food can be used for feeding people and livestock. An example of some areas of the world and the amount of acreage used for the planting of potatoes is as follows. In the United States, it is estimated that 2,000,000 acres are planted with potatoes each year. In the Union of Soviet Socialistic Republics, it is estimated that 28,000,000 acres of potatoes are planted each year. In Western Europe, it is estimated that 16,000,000 acres of potatoes are planted each year. If the spoiling and rotting of potatoes can be reduced by a relatively high percentage by better storage methods and apparatus, it is seen that many tons of potatoes are made available for feeding to human beings and to livestock.